Backlight module is used for providing a light source for a liquid crystal display. The light emitting efficiency of the backlight module affects display quality of the liquid crystal display directly. A pattern or a character displayed on the liquid crystal display is a modulation result of lights emitted from the backlight module. FIG. 1 (a) and FIG. 1 (b) are a front view and sectional view of a backlight module known by the inventors, respectively, FIG. 2 is an enlarged view of part A shown in FIG. 1 (b). The backlight module mainly includes a light reflecting sheet 11, a light guide plate 12, a diffuser sheet 13, a prism sheet 14, a light shielding sheet 15, a sealant frame 16, and a lamp group 17.
At present, the light guide plate used in the backlight module can be divided into two kinds of light guide plates, that is, a flat light guide plate and a wedge light guide plate. For example, the backlight modules as illustrated in FIG. 1 (a), FIG. 1 (b) and FIG. 2 use a wedge light guide plate as the light guide plate 12. However, each of those two kinds of the light guide plates may lead to light leakage. This is because most of light sources used in the backlight module are point light sources. If the point light source is placed too close to a prism sheet, lights may be reflected or refracted directly by prisms on the prism sheet, thus generating strong lights in front of the lamp, which leads to light leakage in front of the lamp.
For example, in FIG. 2, the lamp group 17 is a point light source. The prism sheet 14 and the light shielding sheet 15 typically have an overlapping portion at a position close to the lamp group 17, so that a distance between the prism sheet 14 and the lamp group 17 is small, thus light leakage occurs in front of the lamps. FIG. 3 (a) and FIG. 3 (b) are schematic views showing a light leakage in front of the lamps.
With development of display products to be light weight, compact, and aesthetic appealing, more and more backlight module use the wedge light guide plate to meet compactness requirement. However, the wedge light guide plate may aggravate the light leakage in front of the lamps of the backlight module, resulting in difficult image processing. Thus, the light leakage in front of the lamp is always a difficult and lingering issue to be addressed in a backlight module.